(1) Field of the Invention
The present invention relates to heat insulating ceramic insert-cast articles for use in exhaust channels in internal combustion engines and a process for producing the same.
(2) Related Art Statement
In the case of a system for purifying exhaust gases from internal combustion engines such as gasoline engines and diesel engines and for preventing air pollution with such exhaust gases, it is desired that the temperature of the exhaust gases is maintained high, because reduction in the temperature of the exhaust gases lowers the purifying performance of the catalyst. For this reason, as described in Japanese patent publication No. 51-16,168, it is proposed that an exhaust port in a cylinder head or an exhaust manifold is lined with a heat insulating ceramic liner. Although such a ceramic liner is used as enclosed with a metal such as aluminum or the like, its heat insulating effect is not sufficient because the thickness of the liner is about 2 to 3 mm. As a result, the temperature of exhaust gases merely increases by about 20.degree. C. as compared to the case where no liner is provided.
Under the circumstances, as trial is made, in which fibers made of a refractory material are wound around the outer periphery of a ceramic liner, and then the ceramic liner is enclosed so that heat insulation is enhanced by the fiber layer. However, since the fibers are gradually damaged due to thermal shocks on starting and stopping of engines or due to engine vibrations and heat, they lose the ability to hole the ceramic liner. Ultimately, there is the possibility that the ceramic liner slips out from the fibers. Furthermore, as shown in Japanese Utility Model Registratin Application Laid-open No. 54-56,010, a space is formed by arranging a metallic plate around the outer periphery of a ceramic liner so that a heat insulating property possessed by air may be utilized. However, since the structure is complicated and the production cost is great and since the ceramic liner is held at opposite ends only, there is a problem in that forces for holding the ceramic liner are likely to be lost.